Extreme Programming Programming History 1960s Cowboys wrote software

Extreme Programming

Programming History

1960’s “Cowboys” wrote software anyway that they could Difference between best programmers and worst as high as 28: 1 (many sources) Start of the “software crisis” 1968 Edsger Dijkstra, “GOTO Statement Considered Harmful” (CACM) Recognition that rules can improve the average programmer

Structuring Software Development Few rules helped immensely Good rules and practices developed over the 70’s and 80’s If a few rules are good, more are better… Late 80’s, major focus on process as a key to quality ISO 9000 (first published 1987) Malcolm Baldrige National Quality Award (just celebrated 25 th anniversary)

ISO 9000 ISO: International body 150 national standards organization (US: ANSI) Originally technical standards Has broadened its scope: e. g. , quality ISO 9000: family of standards Generic management system standard Not the process but the management of the process Compendium Continues ISO of best practices to be updated 9001 key standard

ISO 9001 Requirements Business customer requirement based internal audits evaluation and improvements problem management and effectiveness monitoring communication and validation non-conformances and bad product Quality Policy formal statement from management understood and followed at all levels by all employees used to establish employee measurable objectives Quality System regularly audited and evaluated for conformance and effectiveness decisions based on recorded data records that trace raw materials and products to the source

Why not apply to software development? Companies Large documents and people to manage them Rise of the project manager “Honored More started codifying their practices in the breach” large projects and more late or failed projects 1995 Standish Group Study Jerry Saltzer SOSP 1999

1995 Standish Group Study 50% software projects challenged 2 x budget 2 x completion time 2/3 30% planned function impaired Scrapped 20% success

Jerry Saltzer Presentation Who is Jerry Saltzer? Early time sharing (CTSS) Multics Operating System (“inspired” Unix) Project Athena Thin client computing Kerberos LDAP Instant messaging

Software Engineering Processes Differ by how often you Points on the spectrum Differences in overhead Three fundamental Waterfall Spiral Iterative do the steps models Widely used models Integrated Product Development Unified Software Development Process Extreme Programming

All models address the 4 P’s of Software Engineering People: those doing it Product: what is produced Process: manner in which it is done Project: the doing of it

Integrated Product Development (IBM) Originated at GE Cross-functional teams at all phases Phased approval (easy to start, easy to kill) Concept Plan Ship Sunset

Unified (Software Development) Process Iterations within phases 4 phases and core workflows for each Inception Requirements Analysis Design Implementation Test Elaboration Construction Transition

Agile Methodologies: Born from Backlash

Agile Methodologies Keep only those rules and processes that help Antidote to bureaucracy License to hack Key characteristics Adaptive People-oriented

Agile Manifesto February 2001 Representatives from Extreme Programming SCRUM DSDM Adaptive Software Dev Crystal Feature-Driven Dev Pragmatic Programming

Extreme Programming

Extreme Programming Complete development process First code drop 2 -3 weeks after start (what is the start? ) Customer Iterative part of the development team development to the max Derive requirements with customer through hands-on experimentation Agile methodology

History Kent Beck considered the inventor Ideas developed in the early 90’s First project at Daimler Chrysler in 1996 Smalltalk Design patterns Extreme programming

XP Bills of Rights Developer Clear has a right to requirements and priorities Determine how long requirement will take Revise estimates Always produce quality code

XP Bills of Rights Customer has a right to An overall plan See progress in a running system Change requirements and priorities Be informed of changes to schedule and have input as to how to adapt Cancel in the middle and still have something to show for the investment

XP Value System Communication: Focus on people, not documentation Simplicity: Of process and code Feedback: Mechanism to make useful progress Courage: To trust in people what you would like to know about software that life depended on? (Bollinger) your

Extreme Programming Flowchart http: //www. extremeprogramming. org/

User Stories Use cases Written by customer Used for planning Developers Stories Used estimate by story basis for iteration to build acceptance tests Remember: correctness equals meeting requirements

System Metaphor Initial system design

Spikes Technology explorations Focus on high risk items Typically considered throw-away code If not, needs to be agreed to by the whole team

Release Planning Each iteration has its own plan Function OR date (other is adjusted accordingly) (Recall 4 variables: function, date, resources, quality) Planning adapts as the project progresses Measure project velocity Number of user stories and tasks completed Next iteration looks at planned vs. actual time Allowed to plan last iteration’s number for this iteration

Iteration Scope: all parts of the system Only add functions needed for current user stories Recommendation: 3 weeks Moving people around Backup and training Code is owned by the whole team Pair programming Re-factoring

Pair Programming Two people working at a single computer Built-in backup and inspections Collaboration builds better code Mechanical model One drives, the other talks Keyboard slides between the two Logical One model tactical, the other strategic Both think about the full spectrum but bring different perspectives

Pair Programming Experiments Typical numbers: total manpower not very different No more than ¼ additional Implication: actual time reduced Improved satisfaction also improves productivity Williams et al, “Strengthening the Case for Pair-Programming”

Refactoring Each iteration adds just the function needed If you continue to add new functions every two weeks, code can get messy Refactoring is the cleaning up of the code at the end of the iteration Critical (Also to maintaining quality code applies to the design) Difference between refactoring & rewriting?

Feedback Loops

The Rules of Extreme Programming Planning Managing � Designing � Coding � Testing

Rules of Extreme Programming

When to Use XP Types High of projects risk Poorly understood requirements Team Small size: 2 to 12 Needs to include customer Automated Timing testing issue

What Makes a Project XP Paradigm see change as the norm, not the exception: optimize for change Values communication, simplicity, feedback, courage: honor in actions Power sharing business makes business decisions; development, technical ones Distributed responsibility and authority people make commitments for which they are accountable Optimizing process aware of process and whether it is working: experiment to fix acculturate new team members Ward Cunningham, Ron Jeffries, Martin Fowler, Kent Beck

NOT everyone loves XP

References Agile Methodologies www. martinfowler. com/articles/new. Methodology. html Discussion http: //xp. c 2. com/Extreme. Programming. Roadmap. html